Travis Snider has been better than Gregory Polanco this year. Obviously, you don't want to sit Polanco and have a young player with his talent watching games for very long. However, if both players play continue as it has, there could be a case for Polanco returning to AAA and Snider starting in RF to start next year's season.
While this may sound extreme, the Pirates need Polanco's first five years to be good/great years. He won't help us much if his first five years are like Jason Heyward's.